Since the underutilization of technology often prevents organizations from reaping expected benefits from IT investments, an increasing body of literature studies how to elicit value-added, post-adoptive IT use behaviors. Such behaviors include extended and innovative feature use, both of which are exploratory in nature and can lead to improved work performance. Since these exploratory behaviors can be risky, research has directed attention to trust in technology as an antecedent to post-adoptive IT use. In parallel, research has examined how computer self-efficacy relates to post-adoptive IT use. While such research has found that both trust and efficacy can lead to value-added IT use and that they might do so interdependently, scant research has examined the interplay between these antecedents to post-adoptive IT use. Drawing on the Model of Proactive Work Behavior with a focus on its predictions about trust and efficacy, we develop a research model that integrates trust in technology and computer self-efficacy in the post-adoption context. Our model suggests that the two concepts are interdependent such that trust-related impacts on post-adoptive use behaviors unfold via computer-related self-efficacy beliefs. Contemporary tests of mediation on data from more than 350 respondents provided support for our model. Hence, our findings begin to open the black box by which trust-related impacts on post-adoptive behaviors unfold, revealing computer self-efficacy as an important mediating factor. In doing so, this study furthers understanding of how, and why, trust matters in postadoptive usage, enabling strategic change management by elucidating the “fit” between technological characteristics and post-adoptive usage.